As a technique for providing next-generation mobile broadband, Wi-Fi access networks employing a wireless backhaul system are attracting attention. A “wireless backhaul” system is a communication network obtained by wirelessly connecting base stations to each other. With a wireless backhaul system, a wireless relay network (mesh network) is constructed with a core base station as a gateway, each connected to a wired line, thereby covering the service area. With such a wireless backhaul system, a great number of wireless relay base stations are connected to the core base station so as to provide the communication service, thereby suppressing the cost of laying required wired lines. Thus, such an arrangement allows the service area to be expanded and changed with low costs and high flexibility.
The relay line performance of a wireless backhaul system depends on the antenna directionality and installation layout. Typically, a wireless packet forwarding device is installed in a ceiling or on a wall. Accordingly, in many cases, the installation layout is limited by the layout of furniture and fixtures in the building or from the viewpoint of its appearance. Thus, with such a wireless backhaul system, in order to provide stable relay line performance independent of the installation layout or the antenna direction, it is preferable for the antenna directionality to be automatically adjusted according to the installation layout and the like, which is an effective method.
An arrangement employing multiple antennas so as to improve the communication quality is described in Patent Literature 1 and Patent Literature 2, for example. Patent Literature 1 describes an arrangement in which the antenna to be used is selected from among a vertical polarized antenna and a horizontal polarized antenna based on the communication rate of the transmission signal, and wireless communication is performed using the antenna thus selected, so as to reduce interference between signals, thereby providing improved frequency usage efficiency. Patent Literature 2 describes an arrangement in which the wave to be used is selected from among a vertical polarized wave and a horizontal polarized wave based on the measured value of the output of a mobile terminal with respect to the transmission wave, and the wave thus selected is assigned as the transmission/reception wave.